Field of the Invention
The present invention relates to a shaped component for an aluminum alloy turbo compressor wheel used in a turbocharger used in an internal combustion engine for a transportation device such as an automobile and a method of manufacturing a turbo compressor wheel.
Priority is claimed on Japanese Patent Application No. 2013-258638, filed Dec. 13, 2013, the content of which is incorporated herein by reference.
Description of Related Art
It is well known that a turbocharger used in an internal combustion engine for a transportation device is an apparatus in which, when a compressor wheel (also called an impeller) connected to a turbine that is rotated using the pressure of exhaust gas through a connecting shaft rotates, air is sent to a compressor housing and is compressed, and the compressed air is sent into a combustion chamber, thereby increasing the combustion efficiency of the internal combustion engine and thus achieving improvement in the output of the internal combustion engine and the purification of exhaust gas. The above-described turbocharger has a structure in which, generally, a turbine side (exhaust gas) and a compressor side (intake side) are separately provided and an adiabatic bearing is disposed therebetween. In the compressor side, the compressor wheel is disposed in the center of the compressor housing.
The above-described compressor wheel in a turbocharger apparatus generally has a constitution in which, on the outer circumferential side of a rotary shaft portion that generally forms a conical shape, a plurality of thin curved blade portions (wing portions) for rapidly collecting air are radially formed so as to form a part of a whirlpool. In addition, the compressor wheel is disposed in the central portion of a housing including a snail-shaped swirling tube.
As a typical example of a compressor wheel, FIGS. 1 to 3 illustrate an example of the overall scheme of a basic shape thereof, and sections of main parts thereof are illustrated in an enlarged manner in FIG. 4.
In FIGS. 1 to 4, a compressor wheel 1 has a structure in which a plurality of radial blade portions 4 are integrally formed on the outer circumferential side of a substantially conical rotary shaft portion 3 including a shaft hole 2 for press-fitting a shaft that is connected to a turbine-side rotor, not illustrated, into the rotary shaft portion. Here, in the edge portion of the blade portion 4, the edge portion (edge portion) 4A inclined in a twisted and curved shape (inclined in a twisted shape with respect to the rotational center axis line O) between the edge portion 4B on the air-intake side and the edge portion 4C on the air-discharge side is an edge portion forming a gap (so-called tip clearance) between the compressor housing and itself, that is, a portion called a tip edge portion.
The end portion of the rotary shaft portion 3 on the small diameter side serves as a boss portion 5 protruding from the end portion of the blade portion 4. In addition, a portion 7 continuing from the outer edge part (here, mainly, the portion near the boss portion 5 on one end side of the rotary shaft portion 3 is excluded) of the rotary shaft portion 3 to the blade portion 4, in other words, a portion rising from the outer circumferential part of the rotary shaft portion 3 to the blade portion 4 can be called a blade root portion 7. Meanwhile, in an actual compressor wheel, it is usual to provide a finer shape or form additional fine protrusion portions or additional recessed portions in the respective portions; however, herein, only basic parts are illustrated, and a detailed shape is not illustrated. In addition, in the case of a compressor wheel in a turbocharger in a transportation device such as an automobile, regarding the overall dimensions, for example, the maximum outer diameter from the rotation axis line O as a standard is often in a range of approximately 30 mm to 150 mm and the maximum length in a direction along the rotation axis line O is often in a range of approximately 20 mm to 100 mm.
Meanwhile, the compressor wheel in a turbocharger is rotated at high speed of faster than 10000 rpm at high temperature of approximately 150° C., and thus the compressor wheel needs to have high strength at high-temperature and high rigidity and, simultaneously, needs to have low weight in order to reduce energy loss. In addition, the compressor wheel also needs to have a favorable dynamic balance during high-speed rotation so as to withstand high-speed rotation and thus needs to have a uniform density in the circumferential direction (rotation direction).
Additionally, in the compressor wheel, it is effective to transfer heat from the turbine side to compressed air in order to increase the efficiency by means of an increase in the temperature of the compressed air, and thus the compressor wheel desirably has favorable heat-dissipating properties (heat conductivity).
Furthermore, when the respective portions of the compressor wheel are taken into account, the blade portion 4 needs to have a thin thickness (generally a thickness of smaller than 1 mm) in order to ensure a low weight. Therefore, it is desirable that the blade portion 4 not easily deform during high-speed rotation, and thus the blade portion 4 has favorable high-temperature strength and high rigidity, and, particularly, a portion near the tip edge portion 4A at the tip of the blade portion 4 has sufficiently favorable high-temperature strength and sufficiently high rigidity since this portion generally has an extremely thin thickness. Meanwhile, the blade root portion (the portion continuing from the rotary shaft portion 3 to the blade portion 4) 7 is a portion at which stress concentrates during rotation and thus needs to have a high notch fatigue strength in order to satisfy durability and reliability with respect to long-term use during high-speed rotation. The rotary shaft portion 3 is a portion supporting a plurality of the blade portions 4, and furthermore, when a turbocharger is assembled, it is usual to pressure-fit a shaft into the shaft hole 2 in the rotary shaft portion 3. Therefore, it is desirable that the rotary shaft portion 3 have a significantly thicker thickness than the blade portion, and furthermore, the boss portion 5 on one end side of the rotary shaft portion 3 needs to have favorable strength and elongation so as to prevent cracking during the pressure-fitting of the shaft.
As described above, in the compressor wheel, it is desirable that the compressor wheel have high strength at high temperature and high rigidity as a whole, have excellent dynamic balance during high-speed rotation, and have low weight, and simultaneously, the respective portions have different characteristics suitable for the functions, shapes, thicknesses, and the like of the respective portions.
Meanwhile, as a material for a compressor wheel in a turbocharger of the related art, from the viewpoint of, mainly, a low weight or thermal conductivity and, furthermore, processability and the like out of the above-described required characteristics, generally, an aluminum alloy is used.
In the related art, for this type of aluminum alloy compressor wheel, it has been usual that a shaped component is directly cast from a molten aluminum alloy using a casting method called a lost-wax method (also called a precision casting method), and an appropriate finish processing such as cutting is carried out on the precisely-cast shaped component, thereby completing a compressor wheel (for example, PTL 1 and the like).
In addition, as a method of manufacturing a rotary body such as a compressor wheel in a turbocharger, a method has also been proposed in which an extruded aluminum alloy (extruded billet) is used as a material, a forged shaped component is produced by forging the extruded billet, and furthermore, the forged shaped component is cut for completion (for example, PTL 2).
Additionally, in PTL 3, there is a proposal regarding a method in which, with an assumption that this method is a method of obtaining a rotary body such as a compressor wheel in a turbocharger from an aluminum alloy material by means of forging similarly to the case of PTL 2, in this case, an extruded billet is uniformly hardened as a whole in a forging step, that is, is hardened in three directions, thereby obtaining a forged shaped component in which there is no dead zone and a metal flow portion is almost uniformly present.